To obtain a molecular insight into epilespy and develop optimal therapies for seizure disorders, it is important to understand the basic processes regulating neuronal excitability and how pathological processes interact with normal modulatory mechanisms that control neuronal activity. Although the precise molecular aspects of the regulation of excitability are not known, recent advances have been made in understanding the role that calcium, a major second messenger in neurons, plays in regulating neuronal excitability. Ca2+-calmodulin dependent protein kinase (CaM kinase II) has been implicated in regulating some of the effects of Ca2+ on cellular function and neuronal excitability. Studies in this research effort will test the Hypothesis that CaM kinase II is involved in mediating some of the regulatory effects of Ca2+ on specific membrane ion conductances. This project will coordinate biochemical, immunocytochemical and electrophysiological studies to determine whether endogenous CaM kinase II mediates the effects of Ca2+ on specific ion conductances in identified neurons of the nudibranch mollusc, Hermissenda crassicornis. Our Short-Term Goals are a) characterization of the effects of exogenous CaM kinase II on specific ion conductance in identified neurons, b) identification and characterization of endogenous CaM kinase II activity in these neurons, and c) immunocytochemical studies employing monoclonal antibodies to ascertain the cellular and subcellular distribution of CaM kinase II in these neurons. The Long Term Goas are a)investigation of whether neuronal excitation can modulate the activity of CaM kinase II, employing in vivo phosphorylation studies, b) characterization of the effects of monoclonal antibodies that have previously been demonstrated to regulate CaM kinase II activity on specific ion conductances, and c) correlation of the effects of pharmacological agents on endogenous CaM kinase II activity with their effects on specific ion conductances in neurons. The results may provide a molecular insight into an endogenous mechanism for modulating some of the effects of Ca2+ on neuronal excitability and may increase our understanding of the complex mechanisms that underlie the pathogenesis of seizure discharge and its regulation by anticonvulsant compounds.